At present, Active Matrix Organic Light Emitting Diode (AMOLED) display is a focus topic in panel display research. Compared to Liquid Crystal Display, Organic Light Emitting Diode (OLED) has the advantages of low power consumption, low manufacture cost, self illumination, wide view angle and rapid response, etc., and begins to replace conventional LCD display screens in display fields, such as mobile phone, PDA (Personal Digital Assistant), and digital camera, etc. Pixel driving circuit design is a core technique of AMOLED display, and has important research significance.
Different from that Thin Film Transistor Liquid Crystal Display (TFT-LCD) performs luminance control by using a stable voltage, OLED is a current-driven device and requires a stable current to perform luminance control. Due to manufacture process and device aging, etc., in an existing driving circuit comprising two transistors T1 and T2 and a storage capacitor C1 (please refer to FIG. 1), a driving current IOLED is generated by applying a voltage Vdata supplied from a data line on a saturation region of a driving transistor (DTFT). The driving current drives OLED to emit light, and can be calculated as: IOLED=K(VGS−Vth)2, wherein VGS is a voltage across a gate and a source of the driving transistor, and Vth is a threshold voltage of the driving transistor. The threshold voltages Vth of respective driving TFTs of pixels (that is, T2 in FIG. 1) are not uniform due to manufacture process and device aging, etc., thereby the currents flowing through respective OLEDs in pixels changing from one to another, and thus display quality of a whole image is affected.